Rotary drilling rock bits are commonly used to drill boreholes for oil wells, gas wells, geothermal wells, etc., especially where the terrain consists of soft to medium hard rock. Rotary drilling rock bits drill by essentially appplying point loads to the rock with a series of hardened knobs, cutters, protrusions or projections on rotatably mounted conical surfaces. The point loads are of sufficient magnitude to comminute the rock by fracturing, shearing and the like.
In deep drilling, such as to depths greater than about 5,000 feet, high strength igneous rock is frequently encountered. Such rock may effectively reduce or altogether stop the drilling because it has a higher hardness than most other commonly encountered rock formations. When the drill bit's cutting surfaces rapidly wear and its penetration rate decreases from increased rock hardness, the drill must be pulled from the hole to change to bits which provide harder cutting surfaces, such as tungsten carbide or possibly diamond bits. Such required bit changes cause an appreciable amount of down-time and hence economic loss to drilling investors.
Future exploration and development of the energy and mineral resources in the United States and throughout the world will require a great amount of drilling. Much of this drilling will be at great depths and through formations of extremely hard rock. While state of the art drilling technology has been primarily confined to softer oil and gas bearing sedimentary formations, the cost of drilling even this relatively soft rock is expensive. Much future drilling, particularly geothermal drilling, will be in formations having very hard rocks. Therefore, future drilling using state of the art drills will be very time consuming and expensive because of the greater depth to be achieved and the harder rock to be encountered.